Drawn and ironed metal articles, such as can bodies are conventionally formed while carried on a punch through a set of dies including at least one ironing die which thins and lengthens the sidewall of the can body. This operation is repeated through the same set of dies at the rate of more than 100 can bodies per minute. While it is desired that the cups from which the can bodies are formed are uniform and are passed through the dies by a punch carrying the cups along their axes uniformly, the cups are not always uniform and do not always fit onto the punch exactly the same. Thus, the ironing dies must be deflectably mounted so that they may adjust for variations in the cups so that off-centered cups may successfully pass through the dies without damaging the dies.
In the past, ironing dies have been deflectably mounted upon rubber O-rings. These rings are resilient and enabled the ironing dies to deflect in a direction generally perpendicular to their axes of rotation in an amount between about 0.015 and 0.020 inch (0.038 and 0.051 centimeter) from their normally centered position.
Several problems result when using rubber O-rings for this purpose. First, the rings are extruded or molded of rubber. This does not permit the rings to be formed with the fine tolerances necessary to always produce rings which are perfectly centered and sized. Thus, rings which do not meet original specifications must be discarded.
A second problem encountered when employing rubber O-rings as the deflectable mounting for ironing dies results from the lubrication necessary in the die set to form can bodies. Throughout the drawing and ironing operation, the drawing and ironing tools and the cup body are continuously bathed in a lubricant. The lubricant may eventually swell the rubber O-ring out of shape so that the central opening in the O-ring is no longer centered and the ironing dies are not properly aligned with the punch. Thus, frequent replacement of the O-rings is required.
Even if a properly sized O-ring has been provided, and the O-ring has not been affected substantially by the lubricant, the rings do not continually exactly realign the ironing dies after the dies have deflected. Again, due to the nature of the rubber forming the rings, with time the ability of the O-rings to return the dies to their proper alignment position after a deflection is reduced, i.e., the O-rings lose their elasticity. Thus, in addition to the need for replacing O-rings due to their swelling from the lubricant, O-rings must be replaced due to their elastic fatigue with time.
It is thus a primary purpose of the instant invention to provide an improved deflectable mounting for ironing dies in a can drawing and ironing apparatus which may be precisely machined to original specifications such that initial alignment of the ironing dies will result. It is also a primary object of the instant invention to provide an ironing die mounting which will not become substantially elastically fatigued over time either due to the deflection stresses placed on the mounting by the ironing dies or from the lubricant which is used to bathe the drawing and ironing apparatus.